1. Field of the Invention
The present invention relates to telecommunications networks, and particularly but not exclusively to mobile communications networks, and in particular to such a network having a group communications node capable of controlling group communications sessions.
2. Description of the Related Art
Telecommunications networks providing communications services in which group communications sessions supported are known. One such group communications service is group conference calling, in which participants conduct full duplex voice calls with the remainder of the group. Another is a voice dispatch service, in which participants conduct half-duplex communications with the remainder of the group.
An example of a mobile communications system which provides a voice dispatch service, also known as Push To Talk (PTT), is the Motorola™ integrated digital enhanced network, or iDEN™, system. The system includes Enhanced Base Transceiver Systems (EBTSs) at cell sites which link mobile terminals to the fixed network equipment via a radio interface, and which are connected to controlling base station controllers (BSCs). The BSCs provide a link with a switching node that provides conventional circuit switching with a public services telephone network (PSTN), and a Metro Packet Switch (MPS), which provides switching for the dispatch service. A Dispatch Application Processor (DAP) coordinates and controls dispatch communications, by registering the identifications and locations of mobile terminals active in the system.
Conventional cellular communications networks, for example those conforming to the Global System for Mobile Communications (GSM) standard, have in the past provided voice call services via a circuit-switched network. GSM was originally designed to support full duplex, circuit-switched voice calls. More recently, operators of such cellular communications networks have considered enhancing their networks to provide voice dispatch services. There are various options for adding voice dispatch services to conventional cellular communications networks, including a voice dispatch service operating using circuit-switched voice call connections, namely the Real-Time Exchange™ system offered by Kodiak Networks. Other options include providing voice dispatch services over packet-switched network connections, such as General Packet Radio Service (GPRS) connections.
Different mechanisms are known” for charging subscribers for usage of network resources in a telecommunications system. One charging mechanism is for subscribers who enter into a contract with the network operator to pay for usage of network services after such usage, referred to as “post-pay”. For post-pay subscribers, the network switches monitor the duration of calls and generate Call Detail Records (CDRs) containing details of the network usage. Such CDRs are sent to a post-pay billing system, and are then used, at the end of each billing period, to generate a bill which is sent to the subscriber for payment. In this mechanism, the billing system does not control usage of network resources in real-time, but rather generates charges after chargeable events have occurred.
An alternative charging mechanism is for what are referred to as “pre-pay” subscribers. In this mechanism, a subscriber pays for usage of network resources in advance, as a result of which an amount of credit is added to a balance of account held for the subscriber in a real-time charging control system called a “pre-pay platform”, which controls charging for usage of network resources during such usage. For circuit-switched voice calls, the network switches have built-in mechanisms, which use intelligent network (DSf) signalling to interact with the pre-pay platform. During the call, the serving switch interacts with the pre-pay platform gradually to decrement the balance of account held in the credit record for the subscriber, in real-time. If the balance runs out, the pre-pay platform instructs the switch to terminate the call, and in this way controls usage of network resources.
A conventional mobile communications network is schematically illustrated in FIG. 1. A set of mobile switching centres (MSCs) 2, referred to herein as switching nodes, are connected via communication links to a number of base station controller (BSCs) 4. The BSCs 4 are dispersed geographically across areas served by the switching node 2. Each BSC 4 controls one or more base transceiver stations (BTSs) 6 located remote from, and connected by further communication links to, the BSC. Each BTS 6 transmits radio signals to, and receives radio signals from, mobile terminals 8 which are in an area served by that BTS. That area is referred to as a “cell”. A cellular communications network is provided with a large number of such cells, which are ideally contiguous to provide continuous coverage over the whole network territory.
The network includes a pre-pay platform 10, which is connected to each of the switching nodes 2 via signaling links. During a conventional two-way voice call, the switching nodes 2 conduct Intelligent Network (IN) signaling with the pre-pay platform 10 so as gradually to decrement a balance amount stored for the chargeable party for the call during the course of the call.
As mentioned above, a known group communications service is group conference calling. A group conference call service is provided by a group conference call service node 12, which is connected to the switching nodes via circuit-switched voice links. The charging mechanism used during provision of the group conference call service to one or more pre-pay subscribers is illustrated in FIG. 2. Typically, each subscriber dials in to the group conference call service and inputs a conference call identifier to be connected to the other participants of the group conference call. The initiating call leg 14 is set up via its serving switching node 2, and the remaining call legs 16 are set up via their respective serving switch nodes 2 as each other participant successfully dials in. If the initiating party is a pre-pay subscriber, the serving switch node 2 on the initiating call leg 14 performs Intelligent Network (IN) signaling 18 with the pre-pay platform 10 in order to control network resource usage for the initiating party. Further, if any of the other participants are pre-pay subscribers, each respective serving switch node 2 on the other call legs 16 performs Intelligent Network (IN) signaling 20 with the pre-pay platform 10 in order to control network resource usage for each other participant individually, during the call. If any of the pre-pay participants' balance runs out during the call, the pre-pay platform 10 instructs the respective serving switch node to release that participant's call leg.